Human glioma cells induce hyperexcitability in cortical networks

Abstract

Summary Purpose Patients with gliomas frequently present with seizures, but the factors associated with seizure development are still poorly understood. In this study, we assessed peritumoral synaptic network activity in a glioma animal model and tested the contribution of aberrant glutamate release from gliomas on glioma-associated epileptic network activity. Methods In vitro brain slices were made from glioma-implanted mice. Using extracellular field recordings, we analyzed peritumoral epileptiform activity induced by Mg2+-free medium in slices from tumor-bearing animals and sham-operated controls. We assessed the effect of sulfasalazine (SAS), a blocker of system xc− and glutamate release, on spontaneous and evoked activity in tumor-associated slices. Key Findings Tumor-associated cortical networks were hyperexcitable. The onset latency of Mg2+-free-induced epileptiform activity was significantly shorter in tumor-bearing slices, and the incidence of Mg2+-free-induced ictal-like events was higher. Block of glutamate release from system xc− decreased the response area of evoked activity and completely blocked Mg2+-free-induced ictal-like, but not interictal-like events. Significance Control of seizures in patients with gliomas is an essential component of clinical management; therefore, understanding the origin of seizures is vital. This work provides evidence that peritumoral synaptic network activity is disrupted by tumor masses resulting in network excitability. We show that blocking glutamate release via system xc− with SAS, a drug already approved by the US Food and Drug Administration (FDA), can inhibit Mg2+-free-induced ictal-like epileptiform events similar to other chemicals used to decrease seizure activity. We therefore suggest that further studies should consider SAS a promising agent to aid in the treatment of seizures associated with gliomas.

Animal models of tumour-associated epilepsy

“…Thus, they either rely on human cell lines (Campbell et al, 2012), human primary cell cultures maintained in nude, i.e. immunocompromized, mice (Buckingham et al, 2011;Campbell et al, 2015), or on a rat cell Q5 line Senner et al, 2004), with mixed cell lines being used in some cases (Beaumont et al, 1996).…”

“…immunocompromized, mice (Buckingham et al, 2011;Campbell et al, 2015), or on a rat cell Q5 line Senner et al, 2004), with mixed cell lines being used in some cases (Beaumont et al, 1996). Cell lines have the advantage of a relatively easy cultivation under cell culture conditions in appropriate media such as DMEM/F12 (Invitrogen) supplemented with 7% bovine growth serum and glutamine (Campbell et al, 2012), or DMEM supplemented with 10% fetal calf serum and antibiotics . They also have the advantage that they can be labelled stably with e.g.…”

“…They also have the advantage that they can be labelled stably with e.g. green fluorescent protein by transfection (Campbell et al, 2012;Köhling et al, 2006) and hence made visible for e.g. in vitro slice experiments, enabling the experimenter to delineate the tumour mass or even identify single glioma cells.…”

“…5% methylcellulose, 10 l), usually with a total cell number of 2.5 × 10 5 to 2 × 10 6 . This results in tumour growth within 7-15 days to a size of 1-2 mm in diameter, and in the case of neocortically injected tumour cells, in seizures, or at least EEG abnormalities and in vitro hyperexcitability, including spontaneous discharges (Buckingham et al, 2011;Campbell et al, 2012Campbell et al, , 2015Köhling et al, 2006). As it can be inferred form Table 1, one of the main problems of such models appears to be that in most cases, seizures are not being reported, even cursorily under the heading of e.g.…”

Neuronal activity in the glioma microenvironment

“…Of note, glutamate secretion by glioma cells contributes to hyperexcitability of neural circuits in the glioma microenvironment, including promotion of seizure activity (Buckingham et al, 2011; Campbell et al, 2012). This suggests that gliomas may actually enhance their own growth and progression not only via direct autocrine/paracrine effects of nonsynaptic secreted glutamate, but also by enhancing local neural activity, inducing an increase in subsequent release of activity-dependent mitogens by other cell types in the microenvironment.…”